Adenosine is a purine which contributes to intermediary metabolism and participates in the regulation of physiological activity in a variety of mammalian tissues. Adenosine participates in many local regulatory mechanisms, such as those occurring in synapses in the central nervous system (CNS) and at neuroeffector junctions in the peripheral nervous system. In the CNS, adenosine inhibits the release of a variety of neurotransmitters, such as acetylcholine, noradrenaline, dopamine, serotonin, glutamate, and GABA; depresses neurotransmission; reduces neuronal firing to induce spinal analgesia and possesses anxiolytic properties. See A. Pelleg and R. Porter, Pharmacotherapy 10(2), 157 (1990); J. Daval, et al., Life Sciences 49: 1435 (1991). In the heart, adenosine suppresses pacemaker activity, slows AV conduction, possesses antiarrhythmic and arrhythmogenic effects, modulates autonomic control and triggers the synthesis and release of prostaglandins. See K. Mullane and M. William, Adenosine and Adenosine Receptors p. 289 (M. Williams, ed. Humana Press, 1990). In addition, adenosine has potent vasodilatory effects and modulates vascular tone. See A Deuseen et al., J. Pflugers Arch. 406: 608 (1986). Adenosine is currently being used clinically for the treatment of superventricular tachycardia and other cardiac anomalies. See C. Chronister, American Journal of Critical Care 2(1): 41-47 (1993). Adenosine analogues are also being investigated for use as anticonvulsant, anxiolytic and neuroprotective agents. See M. Higgins et al., Pharmacy World & Science 16(2): 62-68 (1994).
Adenosine has also been implicated as a primary determinant underlying the symptoms of bronchial asthma. It induces bronchoconstriction and the contraction of airway smooth muscle. See J. Thorne and K. Broadley, American Journal of Respiratory & Critical Care Medicine 149(2 pt. 1): 392-399 (1994); S. Ali et al., Agents & Actions 37(3-4): 165-167 (1992). Adenosine causes bronchoconstriction in asthmatics but not in non-asthmatics. See Bjorck et al., American Review of Respiratory Disease 145(5): 1087-1091 (1992); S. Holgate et al., Annals of the New York Academy of Sciences 629: 227-236 (1991).
In view of the foregoing, it is readily apparent that (i) adenosine depletion may lead to a broad variety of deleterious conditions, and that methods of treating adenosine depletion may be an extremely useful means of therapeutic intervention; and (ii) methods of inducing adenosine depletion may also be useful in treating conditions such as asthma. Folinic acid is an intermediate product of the metabolism of folic acid; the active form into which that acid is converted in the body. Ascorbic acid is required as a necessary factor in the conversion process. Folinic acid has been used therapeutically as an antidote to folic acid antagonists such as methotrexate which block the conversion of folic acid into folinic acid. Additionally, folinic acid has been used as an anti-anemic (combatting folate deficiency). See The Merck Index, Monograph No. 4141 (11th Ed. 1989). The use of folinic acid in patients afflicted with adenosine depletion, or in a method to therapeutically elevate adenosine levels in the brain or other organ, has heretofor neither been suggested nor described.